Senpai and Kouhai!
by Staye
Summary: "Senpai... Senpai... I wonder if I can one day become as supportive and caring as my Senpai" Thought AE-3803. Thankfully, fate had her covered and gave her the chance to experience being a proper Senpai, by advicing her Kouhai about love! Two-part story.
1. Chapter 1

AE-3803 pushed her cart with Co2, much like every other day, through the long roads of the circulatory system. During one of her delivery routes, amongst the crowd around her, she spotted her loving senpai, AA-5100, carrying a basket with nutrients. AE-3803 ran towards her with extreme joy, hugging her with all her might, she almost knocked both of them down. "Senpai, hello! How have you been? It's been so long!"

Senpai let out gasp in surprise, and put her free hand on AE-3803's head. Patting her kouhai's head softly, she chuckled discreetly. "Come on, it hasn't been a day since we last saw each other. No need to be so dramatic, but it still warms my heart how pure and honest you are when it comes to expressing your feelings." Said the caring Senior Red Blood Cell. "How have your deliveries been going today? Any problems?"

AE-3803 looked up at her Senpai, and, excitedly, shook her head from side to side. "No, no! Everything's been going alright, Senpai. I've been getting better at directions, slowly, but still, better." She stepped away from the hug. "Are you going to the lungs? Let's go together." She said with shiny eyes.

"I'm not going to the lungs, but we can walk together for a while, before I need to take my detour, how does that sound? We can chat along the way too. We haven't had a nice chat for a while, despite seeing each other often." Senpai replied with a tender smile, to which AE-3803 nodded and together they traveled across the veins.

The chat they had was brief, but enough to brighten AE-3803's day. As they parted ways, she stood in place, waving at her senpai until she was completely out of view. Reinvigorated, she continued her delivery route with long strides, and a big smile on her face. In her mind, she wondered if she could, one day, become such a caring and supportive senpai to someone else, just like AA-5100.

"Senpai… Senpai…" Those words resonated on her head, making her giggle as she continued walking, lost in her thoughts. "Senpai!" That last one made AE-3803 realize that the voice wasn't just in her head, as NT-4201 stood in front of her, pouting. "Senpai! Are you deaf?! I've been calling out to you for a minute now, don't you realize that'll make me be late on my errands?"

"Oh, oh! You're my kouhai, NT-chan. It's been a while, I haven't seen you since that blizzard. W-Why are you here?" AE-3803 was happy, but also shocked seeing her again. Even if their time together was brief, it was, still, one of her best memories as an erythrocyte. She assumed her kouhai had move on already, as she, clearly, didn't need any further instruction.

"I-I need help…" She blushed ever so slightly, barely letting out her voice. "A-Are you free later o-on?" She looked at her, eye to eye, hers showing her struggle. AE-3803 was moved by her troubled expression, and nodded rapidly. "Of course! Let's meet here again, once we are done for the day, okay?" She knew that NT-4201 was very serious when it came to work, which is why she decided to hold her questions for when both of them were free.

A small sigh of relief was let out by NT-4201, who merely answered with "Okay, I'll see you then, thank you so much, Senpai." She gave a small bow to AE-3803, and continued her route. Just as she did previously with her own senpai, AE-3803 waved at her until she was lost in the crowd.

" _Okay, this is my chance to be an awesome senpai for her. Just like Senpai is with me. I'll support her in everything she needs. Just wait NT-4201, Senpai's here!"_ AE-3803 thought, getting a bit flustered at the idea of her being a support to NT-4201, who knows the world better than her, was way better at her job, and way more mature. " _Now is not the time for that, I need to help my Kouhai!"_ She slapped her face softly and continued on with her daily tasks.

Hours later, an exhausted AE-3803 was sitting on one of the benches along the road, patiently waiting for NT-4201. She had run through her head everything she could think her kouhai might need help with. Considering her attitude and way of thinking, it had to be something related to work, but why would she would come to her, of all people, for help. Those thoughts kept running wild on AE-3803's mind.

She was about to fall asleep, when she felt someone shaking her shoulder. "Senpai, wake up." The touch was firm, but delicate at the same time. It was NT-4201, who was sitting next to her. "If you're too tired, we can meet tomorrow." She said as she looked down, with the same troubled expression from before. This made AE-3803 spring back to life as she answered. "No. no. I'm sorry, NT-Chan. Tell me, what is it that you need help with, you can trust your senpai!" She put her hand on NT's shoulder.

"W-Well, you see… it's kind of stupid." NT looked down.

"If it's troubling you, then it's not stupid. I'm here for you, so go ahead." AE-3803 said, trying to repeat something similar AA-5100-senpai told her when she was feeling down.

"Okay…" She took a deep breath and then spoke so fast, it was hard to understand. "I'm in love and I don't know what to do!" Then, she covered her face with her hands.

AE-3803 only managed to let out a "Huh?" Shocked by the revelation, and, trying to be a mature and composed senpai, she also took a deep breath, preventing herself from getting flustered. "So, that's what it is, I understand now."

"D-Do you really understand, senpai?" NT's voice was muffled, as her face was still covered.

"W-Well, not completely, this wasn't an option I thought of when I was preparing for this, but I'll do anything in my power to help you. Even if my experience with love is… lacking, to say the least. My senpai might be more helpful, to be honest."

"N-No, there's a reason I wanted to see you. And not anyone else." NT finally uncovered her, still blushing, face.

"Oh, then I'm all ears, NT-Chan." She gave her the most reassuring smile she could offer, which did its job.

"O-okay, I wanted to talk with you because… I'm in love with a neutrophil!" She covered her face again as she couldn't bear the embarrassment of confessing that to her Senpai.

"Wait, whaaat!?"

What it felt like eternity passed since NT-4201 revelation to her senpai, who stood frozen in place, trying to process this new information. The silence made NT even more flustered, leading her to, almost, yell. "Senpai, say something!"

"Uh? Oh, yes, yes. I'm sorry, It's hard to imagine you being in love, NT-chan. But you're still young, and young love is one of the best things one can experience, that's what people have told me, at least." She was trying really hard to be a good senpai, despite being even more flustered than her kouhai. She hadn't had any love conversation with her senpai, or anyone for that matter, so she wasn't sure how to handle NT's sudden request.

"I just needed someone to get this off my mind, since it's all I can think of right now, I can't concentrate during work." NT sounded like she was about to cry, still covering her face.

"No, no, don't cry, NT-chan." AE-3803 didn't know how to handle this, so she, simply, pulled her closer in a hug. "I'll help, don't worry. We'll resolve this love problem, even with my inexperience, so please don't cry, whoever is the lucky one wouldn't want to see you cry, right?" She softly patted her on the back of the head as she spoke.

"I-I'm sorry, Senpai." She pulled back from the hug, regaining her composure.

"So, you're in love with a neutrophil. Which is why you came to see me, right?"

"Yes. Some of my friends are in love, but all of them are between us, Red Blood Cells. Then I remembered you walking around with a neutrophil, which is why I said you're the only one who can help me."

"I-I see, well, I'll more than willing to help, if you…" AE-3803 stopped on her tracks as a revelation flashed through her mind. "Wait, you aren't in love with Mr. U-1146, right?" She asked nervously, almost dropping down her "Senpai-mode."

"Senpai! I'm not that kind of girl!" She said pouting. "I'd never fall in love with my senpai's significant over, that would be pretty rude."

"Oh, you've always been really respectful , I'm proud of…" Once again, another revelation hit her mind. "Wait, what? Significant other?! Nononono, you m-m-misunderstood t-things, NT-chan." The serious and mature "Senpai Mode" was shattered to pieces, as AE-3803 tripped over her words, turning darker than her jacket. "W-we're just f-friends, friends!"

"O-Oh, really? Sorry, senpai!" It was hard to say which one was more flustered at this point, as both were not good at talking love related matters. AE-3803 made an attempt at defusing the situation, trying to keep the conversation about NT's request. "O-Ok, regardless, let's forget about all that. You need help to get closer to this neutrophil, right?"

"Uh huh." She nodded, taking deep breaths to regain her composure.

"Mmm, that'll be hard. My friendship with U-1146 started by accident, we don't really meet, we just bump into each other a lot."

"I see. Well, I've crossed paths with him too. And we've courteously exchanged greetings. He's a good fighter too, and saved me and my friends in some occasions. I'm just too embarrassed to even try talking with him."

"Huh. Now that you've mentioned it, me and U-1146 have met each other throughout our whole existence, and most of the times, he has saved me in one way or another. Would you allow me to ask him for assistance in this too? Only if you want. I know it took you a lot of courage to come up to me, so if you don't feel like it. I understand."

NT-4210 took a moment to consider this. She muttered. "I don't know if I should bother him… he's busy. And I'm unsure if I'm deserving of getting help from both of you." She looked down once again.

"Of course you deserve it! I'll drag U-1146 around if I have to. I'll make sure your smile shines bright, because I know you can make anyone fall in love for you with it." She gave her another tender hug. This time, she heard her kouhai mumble. "Thank you, senpai. You're the best." AE-3803 immediately got teary eyes, but held on to not make her kouhai uncomfortable.

After some minutes of embracing each other in silence, NT-4201 pulled away and said. "Let's meet tomorrow, okay? I'll think of ways we could do this."

AE-3803 nodded and replied. "I'll not rest until I find U-1146 and convince him to help! Even if I have to look around all day. Okay, NT-chan, it's getting late, so I want you to go rest for tomorrow, it might be a big day for you. I don't want to see you tired, okay?"

"Okay!" She stood up and gave her senpai a bow. "Thanks for today, Senpai. I'll take my leave now." After that, she lost herself in the crowd. Being alone once again, AE-3803 finally calmed the nerves from being a legitimate senpai for the first time. She relaxed her body and slumped down on the bench, leaning her head backwards and closing her eyes. She wasn't sure how much time passed while she was in that state. She only heard the familiar voice of her best friend, U-1146. "Yo, working hard? I got tea for you."

 **Afterword**

Hey! Trying to do something a bit different! A longer story as a two-parter, the next part will probably be published 2-3 days after this one. This can still be considered on the same "Timeline" as my other works, despite of not really focusing on RBC with WBC. I decided to pick Kouhai as a protagonist instead, since I think her character is really interesting, and I am a bit sad she hasn't been showcased again in the manga. Plus, I think that showcasing AE-3803's relationship with her in a non-work related matter can be interesting. Plus, who knows who Kouhai's mystery crush will be. Thanks for reading this! And I promise to publish the resolution as soon as I can :D


	2. Chapter 2

"I see. Well, she's still young, right? I don't know how much help I can give, but I'm willing to do it for your kouhai. Look at you, you've matured quite a bit, AE." U-1146 was sitting beside his friend, after listening to AE-3803's request.

"I just tried to be mature, like my senpai. It's really hard, especially when it comes to… personal stuff." She conveniently omitted the part where her kouhai thought she and U-1146 were a couple. "How was your day, by the way? Still a lot of bacteria to fight?"

"Not really, we're in mid-autumn, I'm sure there'll be an increase of germ activity when winter comes." He took a sip from his tea, still reflecting on his recent chat with Eosinophil. A lot of romance going around this year, it would seem. "So, we're going to meet with her tomorrow? I think the best course of action is to ask her who is the neutrophil she fell in love with. Maybe I know him. That would make setting up a meeting easier."

"Oh, right! I totally forgot about that, maybe because of the way you appear to the other cells." She joked.

"What's wrong about my image, huh?" He replied in a similar manner.

"Nothing, nothing" She became slightly flustered. "I don't see you as the most social type of guy."

"Believe or not, I do have neutrophil friends. We hang out whenever there isn't any bacteria to kill."

"Oh, Am I taking time from away those meetings?" Asked the curious Red Blood Cell.

"Nah, you're also my friend, right? I have time for you too. More time actually." He smiled.

"R-right. Anyway, so tomorrow's plan is…?" She looked at the neutrophil with confused eyes.

"Meet with your kohai, see if I know the neutrophil, and if I do, we could set up a meeting after you two are done with work. How does that sound?"

"It sounds perfect! U-1146, you really are my savior! It only took you a couple of minutes to come up with a decent plan. You're awesome!" She looked up at him with a bright smile, but her expression also revealed how tired she was.

"Thanks. But now, let's go rest, okay? You're almost falling asleep already.

"Yes, sir!"

The next day, the two erythrocytes looked for U-1146 during lunch time. They found him where he said he would be. NT-4210 was a bit embarrassed, which made her hide behind AE-3803 as both of them went towards his table.

Once they got there, AE-3803 waved to U-1146 and said. "Here's my kouhai, the little maiden." She giggled and softly pushed NT-4201 to introduce herself. She bowed to the neutrophil. "Hello Mr. U-1146, I am honored to meet you. I know it's hard for you to take time off your day to meet us. Thanks for your help!"

U-1146 stoically nodded, but said with a relaxed voice. "I know this might be embarrassing, discussing this with someone you don't know too well. Don't worry, AE has explained to me all the details, so please, take a seat both of you. Let's chat" He let out a reassuring smile, which made NT-4201 way calmer. This small gesture was observed by an admiring AE-3803. _"Wow, he's so calm and cool, he's already a better senpai than me."_ She thought as she sat next to her kouhai.

"So, I know it might still be weird to chat about this, so let's get straight to the point. Do you know the name of the neutrophil you've fallen in love with?" Asked U-1146, as AE-3803 looked over to her kouhai, holding her hand as a gesture of support. "You can tell us NT-chan."

"H-He's… also named U, but I think its number is 4989?" She showed a soft smiled as she recalled him.

"Wait, 4989? Really?" U-1446 blinked slowly, staring at NT-4102.

"Y-Yes… I-Is there a problem?" The young Red Blood Cell felt intimidated by U-1146's gaze.

"U-1146, you're scaring her?!" She complained at her friend, before looking at her Kouhai. "Don't worry NT-chan, he can be a bit thickheaded, and look mean, but he's a good friend."

"O-Ok…" NT nodded.

"No, no. I was just surprised, what are the chances of that. Remember when I told you I had neutrophil friends? Well, it just happens that 4989 is one of them."

"Really?!" AE-3803 almost jumped from her seat. "Please, U-1146! Help us, we can set up a meeting us four. I'm sure NT-chan would love that, right?" She glanced at her Kouhai.

"I-I'm not sure, I am scared." She looked down.

"We'll be with you, it won't be a date or anything like that. Just four friends hanging out." U-1146 said with a calm voice. "You don't have to confess, or even talk about feelings. No need to rush things."

"I-I see. If that's the case. I think we can try."

"Yes! Don't worry NT-chan, I'll be with you every step of the way, and so will U-1146, right?" She pat the neutrophil on the back with a laugh. "See? I told you this guy was caring and reliable."

"Thank you, Mr. U-1146, you're a great cell." She finally was able to relax and give them a warm smile, which slightly stunned both of her friends, who finally realized how beautiful she was when she was.

"Okay, I have to go soon. So, we can meet after you two are done for work. In this same place, I'll bring 4989 along. Any questions?" U-1146 started to check his belongings, ready to depart soon.

"Uhm, I don't think so. I-I have to be strong!" NT-4201 said with determination.

"Yeah! With that smile, you'll make him fall for you in an instant! Shall we also continue our delivery routes?" AE-3803 stood up, holding on to her Kouhai by the arm.

"Yeah, but I think out routes aren't the same, so I need to go in another direction."

"Oh, I see. Well, try to not think too much about today, okay? Everything will be fine."

"I-I'll try. Once again, thank you to both of you." She bowed to them and turned around, walking away at a quick pace.

AE-3803 let out a sigh of relief. "Well, that went well, right? Let's go, we need to work as well." The both cells marched together. The red blood cell looked up. "Do you have a plan to bring your friend to the meeting?"

"He is a bit goofy, but I'm sure he'll tag along. Now we need to chat about what will we do?"

"Uh? What do you mean?"

"U-4989 is a kind cell, but he's thick as an intestine wall. NT-4021 will have to be the one to, at least, try for the two to meet again, they can't depend in us to keep getting together."

"You're right. So, what should we do?"

"I have an idea, just go along, okay?"

"Okay!" AE-3803 pat him in the back again.

The fateful time arrived, and NT-4201 was visibly shaken, as she sat on one of the tables on the resting area. By her side, her senpai held her hand. "You'll be fine. You are an awesome cell, better than me in many aspects. Be confident in yourself, okay?"

The small speech was enough for the Kouhai to stop shaking, but she was still visibly scared. "I-I can do this, I can do this." She kept repeating, trying to encourage herself. "Thanks, senpai. Honestly, I'm so glad I was assigned as your kouhai." These words had a big impact in AE-3803, but she didn't show it, trying to focus on NT-4201.

From an entrance to the area, the two erythrocytes heard bickering, they soon after recognized the voice of the 2 neutrophil.

"Man, sometimes it sucks to be the first line of defense, we are the ones with the most workload, isn't that right, 1146"

"It's our job to protect the cells. Every time we're needed, we'll be there. So there's no point in complaining, shut up, let me enjoy the little peace that I've have."

"Screw you, man."

"Behave yourself 4989, we're about to meet them."

"Right, sorry."

The aloof U-4989 was following his friend, stretching his arms and yawning. The moment the 4 of them saw each other, AE-3803 could feel the hand of her Kouhai getting tighter. She whispered to her. "Let me take the lead here and just relay, okay?" To which, NT-4201 simply nodded.

"Hello, I don't think I've personally introduced you two to this goof. He's 4989, he might look lazy and aloof, but he's a good friend."

"Hello, Mr. 4989, I'm glad to meet you, I'm AE-3803" She gave him a small wave, and then looked over to her Kouhai.

"Y-yes! I'm NT-4021, p-pleased to meet you." She bowed.

"Oh, I've met you before! How have you been? Still hard at work?" U-4989 sat on one of the chairs across NT-4021, as U-1146 sat next to AE-3803.

"Y-Yes, I am. I try to meet my deliveries as soon as p-possible!"

"Hey, you can't bombard a girl you just met. Take it easy." U-1146 said solemnly.

"But he's right though, NT-chan is one of the most hardworking cells I've ever seen. I'm really proud of her! And I'm glad that we can hang out together." AE-3803 tried to show support for her Kouhai.

"T-Thanks, senpai."

"I see, so why did you bring me here, 1146? It's not like I don't want to. Just curious."

"Can't I just want to hang out with my best friend?" U-1146 replied.

"Aw, aren't you the cutest thing. I'm free whenever" U-4989 mocked his friend.

"I meant her, you idiot" U-1146 pointed towards AE-3803

AE-3803 looked surprised, but then she said. "I'll go get some tea. Does anyone else want one?" To which all of them answered positively. After that, she stood up and walked towards the vending machine. As she did so, she walked behind U-4989's chair. She gave a thumbs up to her Kouhai and signaled something to her best friend, who seemed to have got the message.

Minutes passed as, mostly, the two neutrophils bantered to each other, with the occasional interjection from NT-4201. Slowly, she was calming down. U-1146 noticed and decided it was a good time to stand up and say he forgot something, promising to return soon after. Instead, he went to the place AE-3803 was spying from, joining her.

"Are you sure she'll be alright?" He asked.

"I trust in her, even if she looks flustered, she has nerves of steel. Let's just observe for now, and if the situation seems weird, we go back." AE-3803 said confidently.

"Okay."

From a distance they observed the other two cells' interactions with each other. U-4989 seemed to be completely used to being with NT-4201 at this point, who timidly began to smile as the two chatted.

More time passed, from their little hideout, they saw as NT-4201 blushed a bit, but had a beautiful smile as she nodded. After that, U-4989 stood up and gave her a big wave as he left. AE-3803 and U-1146 almost tripped over themselves when they ran back to the table.

Once they got back, they were welcomed back by a silent, but smiling NT-4201. "So, how did it go?" Asked AE-3803. Only to be answered by her Kouhai jumping off her chair and reaching to her for a big hug. In between laughs, she said. "He wants us to see each other again, Senpai. He said I was really fun to chat with!" She was beside herself.

AE-3803 hugged back with a big smile. "See? I told you that things would go well, who wouldn't want to meet again with you. I told you before, if you believe in yourself, things will go well in your life." NT-4201 kept giggling out of joy for a while as she hugged her senpai.

"I hate to be a fun killer, but don't you have deliveries to make? Now that this whole weight has been lifted from your shoulders, I don't want you to go around slacking on your work, okay?"

"Okaaaay." She pulled from the hug and then looked at U-1146, bowing to him. "Thank you, thank you so, so much. I wouldn't have been able to do this without you two. See you later, okay?"

"Okay" The neutrophil saluted her as she dashed away, still over the moon.

"Young love, huh? It can truly transform a person. I have never seen her that happy before." AE-3803 giggled.

"That bastard 4989 won the lottery with her. I'll make sure he doesn't play with her. I promise that."

"Those two are kind of made for each other… Well, I guess I have deliveries to make too. I'll be seeing you, U-1146." She said as she started to walk away.

She was some meters away already when she heard.

"What about us?"

"Huh?" She said as she turned around.

"D-Do you want to go on a date?"

"Oh, sure." She turned around, and kept going for a few steps, before turning around and saying softly. "Wait, what?"

"Let's go to the lake whenever you're free. I know you haven't seen it yet, right?" U-1146 was seriously shocked by her reaction. It wasn't like her at all. There surely would be some yelling, he thought.

"W-Well, if I am counseling my Kouhai about going on dates, it would be immature to refuse one myself, right? See you later, U-1146. At the lake" She gave a peaceful smile as she turned around and walked away slowly.

"Uh, y-yeah. See you." U-1446 was taken aback by this display. _"I guess this whole deal with her kouhai helped her grow as a person. I'm glad."_ He grabbed his tea and sat back down on the chair, looking at her friend, walking away in the distance.

" _OH NO! WHAT WAS THAT JUST NOW! WHAT DID I GET MYSELF INTO THIS TIME?!"_ As soon as she turned around, AE-3803's smile shifted into a face full of terror. " _ME AND U-1146, ON A DATE?!"_

 **Afterword:**

Second part finished! It was way more fun than I thought. I do have more stories in mind when it comes to Kouhai and 4989, so don't worry if their interactions were brief during this. Thanks so much for reading! :D


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